1. Field of the Invention
The present invention relates to an underwater floating up guide device. More specifically, the invention relates to an improvement for a device for guiding a diver in floating up at a constant speed when the diver floats up in the water.
2. Description of the Related Art
As is well known, many people enjoy diving in the ocean or in fresh-water bodies. When the diver floats up to the surface of a body of water, he is required to float up at a constant, predetermined speed. This is because the diver has to moderately exhaust nitrogen gas accumulated in the body while under water in order to avoid suffering from "the bends".
The floating up speed has been conventionally set at approximately 10.about.18 m per minute in order to effectively exhaust nitrogen gas from the body of the diver. Therefore, a study has been made for means for enabling the diver to float up at the constant speed of approximately 10.about.18 m per minute.
One of such means is a floating up guide device. The floating guide device is a device designed to float up from underwater toward the water surface at a constant speed. The device is used in such a manner that the diver releases the device in the water. Then, the floating up guide device floats up toward the water surface at a constant speed. The diver then floats up while targeting the floating up guide device so as to maintain constant separation from the device. Namely, the diver floats up and is guided by the floating up guide device. By setting the floating up speed of the floating up guide device at approximately 10.about.18 m, the diver may float up and effectively exhaust the nitrogen gas accumulated in the body.
Here, discussion will be given for the conventional floating up device. The conventional floating up guide device is disclosed in Japanese Unexamined Patent Publication No. 58-150598. The disclosed device includes a safety valve designed to automatically discharge the content in a balloon when a difference of pressures between inside and outside of the balloon reaches a predetermined value.
In further detail, the floating up guide device includes a hollow space defined in an external wall portion. The external wall portion forms the balloon. When a gas is blown into the interior of the balloon, the hollow space is formed by expansion. In an opening portion of the balloon, a blowing inlet and, as well, a discharge outlet are defined in communication with the hollow space. A safety valve is mounted in the discharge outlet. The safety valve is controlled by a spring provided in series with the safety valve. The spring force of the spring determines a discharge amount of the gas in the balloon.
Discussing the manner of use of the above-mentioned floating guide device, at first, a gas is blown into the balloon through the blowing inlet. This gas is blown into the interior space of the balloon by exhaust gas of the diver or by means of a gas generator, such as a gas bomb and so forth. When a certain amount of gas is blown into the balloon, the floating up guide device is released. Soon after beginning to float upwards, the gas expands inside the balloon due to a decrease of the water pressure. Thus, a predetermined amount of gas is discharged in response to expansion of the gas. By this, the gas pressure in the balloon is controlled to maintain the volume of the gas constant. Therefore, a constant floating up speed can be attained irrespective of the initially blown gas volume. Then, the diver floats up while targeting the floating up guide device and maintaining a constant separation therebetween.
With the above-mentioned prior art, the following defects or drawbacks can be encountered. Namely, at first, the balloon is formed of a relatively soft material to have an elasticity. Due to the elasticity, the balloon may be expanded due to the pressure difference between inside and outside the balloon. If the balloon is expanded by the gas pressure therein to cause variation of its volume, the floating up guide device cannot float up at the constant speed. Therefore, in order to attain the constant floating up speed, an additional mechanism (concretely, the safety valve) must be provided. Secondly, since the discharge amount of the gas in the balloon is determined by the strength of the spring provided in series with the safety valve, the floating up speed of the floating up guide device is variable depending upon the strength of the spring. In other words, the floating up speed of the floating up guide device must be set by the strength of the spring. However, installation and removal of the spring is not so easy, so that one set on the water should be carried into the water for use. Therefore, when the diver wants to set the floating up speed of the floating up guide device within the preferred range of 10.about.18 m, adjustment cannot be easily performed or in the water. Thirdly, before starting use, the conventional device requires blowing of the gas into the balloon. The operation to blow in the gas into the balloon is troublesome and cumbersome work. In addition, this operation should be done for every dive, which make use of such device impractical.